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16 Figure 14. Influence of depth on shear capacity. shear resistance is taken as proportional to the square root of of diagonal compression is at 45 degrees whereas, as these the cylinder compressive strength f c. Figure 15 presents figures illustrate, axial compression increases the number of some of the test data by Moody et al. in 1954 (42) from stirrups that carry the shear across diagonal cracks while which the permissible design stress limit of 2 fc was devel- axial tension decreases the number of stirrups that are avail- oped. The test beams were typically around 14 inches deep, able to carry the shear across cracks. overly reinforced in flexure, and contained large aggregates. Also shown in this plot are the results from a series of tests by Angelakos in 2001 (43) conducted at the University of 1.2.5 Experimental Test Data Toronto on larger and more lightly reinforced members cast The previous examples illustrate the importance of evalu- using smaller size aggregates. As the results in Figures 14 ating and calibrating any potential simplified provisions with and 15 show, the apparent safety of the traditional equation extensive experimental data. Professors Reineck and for 2 fc as used in U.S. practice for beams without shear Kuchma (46), and their research assistants have assembled reinforcement is also dependent on the parameters of beam what is probably the largest available database of results depth, concrete strength and maximum aggregate size, not from shear tests on structural concrete members. The data- considered in that expression. base contains more than 2000 test results. This database can be mined to assess the accuracy and limitation of all prospec- tive code approaches. Influence of Axial Loads The influence of axial compression and tension on shear 1.2.6 Analysis Tools capacity is examined in Figures 16 (44) and 17 (45). As shown, traditional U.S. design practice expressions can be In addition to experimental test data, analytical tools can both conservative and unconservative. Part of the explana- be used to predict the capacity of prestressed and non- tion for these shortcomings is the assumption that the angle prestressed concrete members. These tools are particularly